Metabolomics elucidating the effect of water activity on the thermal resistance of Salmonella in wheat flour.

With mounting evidence indicating an enhanced thermal resistance of Salmonella at lower a, the effectiveness of thermal treatment in wheat flour decontamination is challenged. Therefore, this study was carried out to evaluate the thermal resistance of three Salmonella strains, including Enteritidis (ATCC 13076), Typhimurium (ATCC 14028) and Newport (ATCC 6962), at 65 °C in wheat flour at three a levels (0.33, 0.53 and 0.69), and to explore the mechanisms of the difference in thermal resistance via nuclear magnetic resonance (NMR)-based metabolomics. The results showed that except for the insignificant difference between the reductions of S. Newport at 0.53 and 0.69 flour a (P > 0.05), a remarkable decreasing trend in Salmonella cell reduction with decreasing flour a was observed after the 20-min thermal treatment. By comparing the metabolic profiles of each strain recovered from the lower-a (0.33 or 0.53) flour with that from the a-0.69 flour, the metabolic differences implying more efficient misfolded protein degradation, higher availability of amino acids as osmoprotectants, larger throughput of energy production by ATP synthase as well as wiser glucose allocation in the metabolic network were suspected to contribute to the strains' enhanced thermal resistance. Overall, the study adds to the evidence for the effect of lower a in increasing the thermal resistance of Salmonella in wheat flour. Meanwhile, the identified discriminative metabolic pathways may be artificially modified in the future to help ease Salmonella inhibition during cooking or any types of thermal treatments.